good is relative...a cube won't harm you much anymore if you drain 70% of his weapon power and shield power...but his HY torp is still dangerous. the surplus power allways helps you in return. another problem i see is, that appart from stfs there are hardly any enemies that live long enough to see the end of a siphon.
definately better suited for PVP, but far from useless in PVE, just that there are not many opportunities to use them appart from stfs.
Would put more sci feel into it, but atm it's my sci officers for my odyssey, so I just threw it together with a MURSV as a troll-boat. Turns out I got trolled by my own ship when it turned out to be incredibly effective, and as a result, was upgraded to a FRSV. Whadya know XD.
Try running a full polaron build with the Jem'Hadar set. Next to the 7.6% extra dmg the 3rd bonus also is a shield killer. Try running GW3 and Vent Theta Radiation with that and watch those NPC suffer :p
In order: Gravity Well 3 -> Anti Proton Sweep (3rd bonus) -> Evasive Maneuvers -> Vent Theta Radiation -> Torp spread 2.
I do this in an Intrepid and it works pretty good.